Qt/Cocoa sometimes crashes with setUnifiedTitleAndToolBarOnMac(true) (with Testcase)

Please compile the attached testcase (please try the first one, I don't know how to get rid of the second one) with Qt 4.5/Cocoa and 4.6/Cocoa

Press Ctrl+Q and hold it down. This will destroy the MainWindow an create a new one immediately. After few seconds the application will crash.
This is of course just a way to demonstrate the bug but the same crash happens in "real" applications too (that destroy/recreate a QMainWindow).

There's a workaround in the destructor that disables the unified Toolbar before destroying the windows.